Transformer apparatus

ABSTRACT

A transformer is provided in which the primary and secondary windings are wound in the form of a rectangular tube and are mounted spaced apart on the same core leg; at least one outer yoke leg is provided which is joined at its end to the aforesaid core leg to form a closed magnetic path or loop; cutaway portions or gaps are formed in each end of the yoke leg to form a space between a portion of the core leg and the yoke. The primary and secondary windings substantially fill the space or window formed between the inner periphery of the core leg and yoke. In addition an insulating tube is mounted on the core leg in between the primary and secondary windings and the core lamination. This insulating tube is of a length which extends beyond the windings and into the cutaway portions. In addition a lining of insulating material is disposed lining the inner periphery of the yoke to insulate the windings further and extends into the cutaway portion.

United States Patent [72] lnventor Arnold J. Libel-man 2,578,395 12/1951 Brooks 336/165X Skokie, Ill. 2,686,906 8/1954 Schevtchuk 336/ 155 [211 App]. No. 852,799 3,038,135 6/1962 Feinberg 336/165 2% :"f t d g is Primary Examiner-Thomas J. Kozma l a i e Attorneys-Alan C. Rose, Alfred B. Levine, Ronald W. Reagin [73] Assignee Litton Precision Products Inc. and Ronald M G 01 dman Beverly Hills, Calif.

ABSTRACT: A transformer is provided in which the primary and secondary windings are wound in the form of a rectangu- [541 TRANSFORMER APPARATUS lar tube and are mountedspaced apart on the same core leg; at least one outer yoke leg 18 provided which 18 oined at its end 6 Claims, 6 Drawing Figs.

- to the aforesaid core leg to form a closed magnetic path or UaS- loop; cutaway portions or gaps are formed in each end of the 336/178, 336/2 yoke leg to form a space between a portion of the core leg and III- the yoke The and sgcondary windings ubstantially the pace or windgw formed between the inner 165, 178,212 of the core leg and yoke. In addition an insulating tube is mounted on the core leg in between the primary and seconda- [56] References Cmd ry windings and the core lamination. This insulating tube is of UNITED STATES PATENTS a length which extends beyond the windings and into the cu- 2,2l2,l98 8/1940 Sola 336/165X taway portions. In addition a lining of insulating material is 2,413,201 12/1946 Tillman 336/ 165 disposed lining the inner periphery of the yoke to insulate the 2,494,579 1/1950 Pimlott et al. 336/165X windings further and extends into the cutaway portion.

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WI IIi/IIII 3 /f a 10 if 1 TRANSFORMER APPARATUS invention relates to transformers; and, more particuture which completes the loop or flux path, one on each side ofthe middle leg. In one type of transformer, notably ballast tranaformers in arc discharge lighting equipment, the primary and secondary windings are physically in the form of a rectangular tube made up of layers of wire, and these windings are mounted around the center leg and are thereon spaced apart. Often the windings are separated by a flux shunt leakage gap consisting of ferromagnetic material located between windings and projecting from an outer yoke leg to within a predetermined distance of the center leg.

Theoretically the electrical windings and magnetic core are all that are necessary to perform the function of a transformer.

As a practical matter additional elements are necessary: lnsulation' which electrically insulates the coil windings from the iron material, of the magnetic core must be provided. In ballast transformers the primary and secondary transformer windings hold electrical voltages which differ from the electrical potentialof the transformer coreand from eachother by, depending design and application, hundreds of volts ormore. Accordingly, it is necessary to electrically insulate the center leg of core on which the primary and secondary coils are mounted from those windings and to electrically insulate the outside of the windings from the outer core legs so as to prevent any possible electrical short circuit therebetween. ll ii I a er a such as xe pr at d P p fiberglass, asbestos, Nomex or cardboard are satisfactoryv ai hs-tr m.-

On "layer-wound" coils insulation practices include winding eachcoil within the form of a cylinder or rectangular tube inlwhich a first layer of wire is wound onto an insulating tube and the layer is covered with sheet insulating material; a second layer of wire is wound atop the insulating material and this layer is in turn covered with a layer of sheet insulating material; and so on, until the requisite number of layers and turns areformedand an outer wrapping of. insulating material isjapplied last. Since a layer of paper or other insulating materialis used with each layer of wire, there is generally extending fromthe side edges of the complete coil some overlapping insulating material. In addition, the centerleg of the magnetic circuit iscovered with an insulator tube, and the windingswithin the windows are mounted over that tube as a protective measure.

Precision wound coils are made without the additional layers ofipapcr insulating material between each layer of wire. Inthis typeof coil a first layer of wire is wound onto the mandrel ortube-the turns of the subsequentlayer are nestled between the turns of the first layer andso on with each subsequentlayer of wire. This construction increases the density of the coil, reduces coil size, and provides a much higher copper to space ratio than is available with the layer wound coil.Theinsulating techniques used with precision" wound coils include an insulating core tube, a peripheral wrapper and an end turn insulator. These insulators spaced the coil from theedge of the core tube to minimize danger of flashover.

Present insulating practices for transformers with precision wound coilsrequires that a wedge of insulating material be inserted into the window between a side leg of the transformer core and the side of the coil so as to rigidly position the windings and prevent contact between the coil sidesand the side leg. In assembling the winding onto the laminations the wedgeis driven into place. In so doing this places some stressupon the windings. With wide precision coils it is difficult to force the wedge in the window space of a given transformer core. In the least the process is time consuming and, hence, a more expensive operation.

Moreover, while the techniques used for the layer wound and precision wound coils differ, there are similar problems. In both constructions the outer turns of the lowermost windings appear at the comer of the lamination window, the juncture of the central core leg and an outer leg of the transformer lamination. At this location the danger of the flashover" between the windings and the lamination is greatest. Present transformer constructions do not minimize that danger.

It is the magnetic parts and current carrying windings which detennine the power handling capacity of a transformer. All other parts or requirements are provided or made for reasons ancillary to power handling capacity require extra material, labor or space and thus serves to increase manufacturing costs.

Accordingly, it is an object of this invention to provide a transformer construction in which the primary and secondary windings are insulated from the side legs of the transformer core without the use of inserted insulating wedges.

It is an additional object of the invention to provide a transformer structure which permits the assembly with insulation of physically larger electrical windings in a given size of window space than has heretofore been possible without reduction in electrical insulation ratings.

It is a further object of the invention to provide a transformer construction in which the danger of flashover between the core and windings is minimized without reduction in transfonner power handling capacity.

It is another object of the invention to provide a transformer construction procedure for assembling and applying insulation to transformer windings in a more efficient manner than that which has heretofore been possible.

Briefly, in accordance with the invention, a transformer is provided in which the primary and secondary windings are wound in the form of a rectangular tube and are mounted spaced apart on the same core leg; at least one outer yoke leg isprovided which is joined at its end to the aforesaid core leg to form a closed magnetic path or loop; cutaway portions or gapsare formed in each end of the yoke leg to form a space between a portion of the core leg and the yoke. The primary and secondary windings substantially fill the space between the inner periphery of the core leg and yoke. In addition, an insulating tube is mounted on the core leg in between the primary and secondary windings and the core lamination. This insulating tube is of a length which extends beyond the windings and into the aforecited cutaway portions. In addition a lining of insulating material is disposed lining the space between the primary and secondary windings and the inner periphery ofthe yoke and extends into the cutaway portion.

The foregoing and other advantages and features which are believed to be characteristic of the invention both as to its orcore 3 in FIG. I;

The transformer of FIG. 1 includes a primary coil 1 and a secondary coil 2 mounted on a magnetic core 3 which is assembled with a pair of similar yokes 4 and 5. The core and the yokes each comprise a similar number of transformer steel laminations stacked together and held in assembled relation in any desired manner. In the transformer illusn-ated in FIG. 1

, the core and the yokes each comprise a stack of approximately 50 laminations having an overall thickness on the order of 1 A" Yoke 4 includes a pair of end legs 6 and 7 and an intermediate shunt leg 8, joined by a longitudinally extending leg9. Yoke includes a pair of end legs and 11 and an intermediate shunt leg 12 all joined by a longitudinally extending le 13.

The two sets of preassembled yokes 4 and 5 are assembled with the preassembled core 3 on which the primary and secondary windings have been mounted to form the transfonner and are held in assembled relationship in any desired manner. The shunts 8 and 12 extend from the legs 9 and 13, respectively, to

within a predetermined distance of core 3, leaving slight air gaps.

The primary and secondary coils extend through rectangular windows formed between the central core 3 and the yokes 4 and 5 are bounded by the shunt 8 inner surface formed by the stack of laminations. These windows so formed include that formed by the end leg 6 on the upper side of core 3 in one case; the shunt 8 and the leg 7 on the upper side of core 3 in a second case; the leg 10 in shunt 12 on the lower side of core 3 in a third case; and the shunt l2 and leg 11 also on the lower side of core 3 in the last case. The yoke legs and their inner surfaces are substantially perpendicular to the central core leg 3 and its upper and lower window facing inner surfaces.

As is apparent in other transformer constructions, the projecting shunt legs 8 and 12 are deleted to eliminate the magnetic shunt. In such a construction the windows referred to would be essentially only two in number: one of which is formed between central core 3 and yoke leg 4 and yoke legs 6 and 7 on one side of central core 3 and on the other side of core leg 3 between central core leg 3 and yoke leg 13 and yoke legs 10 and 11 of core leg 3. First and second cutout portions or recesses 15 and 17, are formed in yoke legs 6 and 10, respectively, of yokes 4 and 5, respectively, on the left side of the transformer shown in the FIG.

FIG. 2 illustrates in greater detail the construction of cutout portion 15. The cutout portion extends from a predetermined point 19 on the inner surface 20 formed by the stacked laminations of yoke legs 6. From this point the path is defined by a straight line which continues away from the window into yoke leg 6 to a point 21 substantially plane with the plane 22 of the upper inner surface 23 formed by the stacked center legs 3 of FIG. 1. The path of the cutout portion continues from point 21 in a straight line along plane 22 to a point which is plane with both the surface 23 of central core leg 3 and the plane 25 of inner surface 20 of yoke leg 6. As is apparent, surfaces 20 and 23 are substantially perpendicular to one another. With laminations for the central core and yoke legs of the geometry shown in FIG. 1, the cutout portion 15 is formed simply by cutting off the edge of yoke 6 from points 19 to 21 when the laminations are being stamped out from sheet material.

In like manner the cutout portion 17 in yoke 5 is formed. That is, cutout 17 is defined by a path from a predetermined location on the inner surface 26 of yoke leg 10 in a straight line into the leg and away from the window to a second point plane with the second inner surface 27 of core 3, and then along the plane of core 3 back toward the window to a point a point plane with surface 31. A second cutout portion or notch 32 is fonned in leg 11 of yoke 5 which extends from the inner surface 33 of leg 11 away from the window and into leg 11 a predetermined distance to a point substantially plane with the plane of the inner surface 27 of central core leg 3 forming the notch and from thence along the plane of surface 27 back to a point plane with surface 33.

A layer of insulating material 35 is positioned in between the yoke inner surfaces and the primary winding. This insulting material 35 forms an insulating liner around the inner surface partially bordering the window of yoke leg 4 in between the primary and secondary windings and the yoke. Preferably the insulating layer extends at one end withinthe cutaway portion or notch 30 at the other end into the cutaway portion 15. A second layer or strip of insulating material 36 is located between the primary and secondary windings and the inner surfaces of yoke 5 to form an insulating liner therebetween. Likewise, insulating layer 36 preferably extends at one end within notch 32 in yoke leg 9 and at the other end into cutaway portion 17.

A layer of insulating material 37, shown in section in FIG. 1, is wrapped around or surrounds the central core leg 3. The insulating layer 37 is suitably in the form of a tube which is simply inserted over the central core leg and is of a length greater than that distance between the inner surface 20 and inner surface 31 of yoke legs 6 and 7 and, likewise, it is greater in length than the distance between the corresponding inner surfaces 26 and 33 of yoke legs 10 and 11 so that it extends at least into cutaway portions 15 and 17 and, in addition, into notches 30 and 32.

The primary and secondary windings 1 and 2 have the physical geometrical configuration of a cylinder containing a cylindrical passage therethrough. That cylindrical passage is 35 just large enough to fit over insulator tube 37. Accordingly,

each of the coils may be inserted onto the central core leg 6 over the insulating tube 37 and fixed in position. In addition, the size of the primary and secondary windings is large enough to fill substantially the available window space allowing for the insulation.

The yoke and leg laminations are stacked together and individually assembled. Insulating tube 37 is inserted over the central core leg 3 and the secondary 2 and primary 1 windings are inserted over the insulator tube. Strip insulator lining 35 is applied around the inner surface of yoke 4; and strip insulator lining 36 is applied around the inner surface of yoke 5. The yokes are then joined to the core 3 with tube 37 extending into the cutout portions of the yokes and the windings spaced to permit assembly. The complete assembly is then held together and completed in any conventional manner.

In FIG. 3 a transformer which embodies the invention is put together with conventional laminations resembling the capital letters T and F. The central core leg 40 is integrally formed with a transverse portion at one end and together resemble the letter T"; whereas, the yoke legs 44 and 46 have integrally formed therewith in the lamination the magnetic shunts 48 and 49 and a top transverse legs 50 and 51 which completes a configuration resembling the letter F." When assembled together, the completed magnetic circuit and coil windows formed in FIG. 3 are essentially the same as that illustrated in the construction of FIG. 1. However, in FIG. 3 the central core leg 40 may be considered to be bounded by the imaginary lines 52 and 53 with the transverse portions being considered functionally a part of the yoke legs 54 and 55 even though physically those legs are formed integrally in a single lamination with central core leg 40. A yoke provides a return path for magnetic flux generated in coil windings around a core that this flux path in FIG. 3 proceeds from the left end of core 40 through legs 54, 44, and 50 to the other end of core 40. Some of this flux however is shunted through shunt 48. Likewise, another yoke provides a flux path through legs 55, 46, and 51 with some flux shunted through shunt 49.

Leg 54 contains a cutout portion 57 and leg 55 contains a cutout portion 58. These cutout portions are formed in the respective legs in a structural relationship as has been set forth in the discussion of the structure of FIG. 1.

' In like manner, leg 50 contains a cutaway portion or notch corresponding to the insulating tube 37 of FIG. 1 is mounted along center core leg 40 and extends into each of the cutaway portions 57 through 60. The primary and secondary windings are mounted in and substantially fill the window locations corresponding to those shown in F IG. 1.

The transformer laminations in FIG. 4 represent another familiar configuration which is modified so that it incorporates the subject matter of this invention. This lamination configuration is the familiar E-I configuration in which one lamination 62 is integrally formed in the shape of the letter B, and the cooperating lamination 64 is formed in the shape of the letter T.'In this the central core leg 66 considered to consist of two sections bounded by imaginary lines 67, 68, 69, and 70 and the remaining portions of both laminations being conside-ed the yoke. Accordingly, the E lamination 62 includes legs 72, 73, 74, and 75 and I lamination 64 includes legs 76 and 77.

Cutout portions 80, 82, 84, and 86 are formed in lamination 64 and are constructed in accordance with the design discussed with respect to the cutout positions of FIG. 1. The transformer of this FIG. does not include a magnetic gap. In the complete transformer the insulating layers which line the inner. surfaces of the windows and which preferably terminate in the cutout portions and the insulating tube around the central core leg which extends preferably into the cutaway portionson the right and left sides of the transformer is provided. These elements have been amply described in connection with FIG. I.

F 16.5 illustrates another lamination configuration using an E lamination 90 and an I lamination 91 similar to that of FIG.

4. However, the transformer in this configuration the middle stem 92 of the E and forming part of the central core leg is 'foreshorted so as to be spaced physically from the I lamination by an air gap 93. The gap 152 is generally conventional and is provided to increase the reluctance of the magnetic circuit.

In this FIG. the central magnetic core leg may be considered to be bonded by the dashed lines 94, 103, 96, and 101 and includes air gap 93. The remainder of the laminations or legs perform the function of a first and second yoke. Cutaway portions 97, 98, 99, and 100 are provided in accordance with the requirements and limitations discussed with respect to FIG. 1. Likewise in the completed transfonner, the coils, insulating liners, and insulator tube surrounding the central core leg is provided. However, this structure has been amply discussed in the preceding FIGS. and need not be considered again in detail.

' In FIG. 6 an ignition transformer which embodies the invention is illustrated. The transformer includes an E lamination, 102, and I lamination 104, a primary 106, and a secondary winding 108. The insulating tube 110 extends into the formed notches with insulating liner 1 12.

In the transformers it is apparent that due to the cutaway portions and insulator tube adequate insulation is provided. The opportunity for the electrical coils to be pinched or electrically shorted to the magnetic laminations, especially at the juncture of the central core leg with a transverse yoke leg is completely eliminated.

Fortuitously, the inclusion of the cutout portions in transfonners using the principles of this invention increases the magnetic reluctance of the fiux path in a permissible amount without adversely affecting the performance of the transformer. Often air gapsor bridged gaps are included in the magnetic flux path in the transformers laminations, such as was illustrated in FIG. 5. These air gaps are provided to obtain certain electrical results. In those transformers the invention is especially helpful to the overall results desired to be achieved.

The cutaway portions may be as large as practicable so that they may accomplish the functions of an air gap or bridged gap in addition to their usefulness in achieving the present objects of my invention.

It is understood that the above described arrangements are intended to be illustrative of the invention and are not intended to limit the invention since numerous equivalents suggest themselves to those skilled in the art which do not depart from the spirit and scope of the invention. It is to be expressly understood that the invention is to be broadly construed within the spirit of the appended claims. lclaim:

1. A transformer comprising:

a. A magnetic core having a completed configuration of a center, first outer and second outer legs spaced apart and parallel, and a first and second side leg spaced apart, parallel, and joining with said center first and second outer legs to define at least two generally rectangular windows one above and the other below said center leg; said center first outer and said first and second side legs having an inner surface bordering one of said windows, said central second outer and first and second side legs having an inner surface bordering said other window;

b. first cutout portion in one of said side legs defined by a path which extends from a predetermined point along the inner surface of said side leg and proximate said center leg into said side leg and away from said window a predetermined distance, then along to a point substantially plane with the inner surface of said center leg and spaced from said inner surface of said side leg, and thence back along the plane of said central leg to a point plane with the inner surface of said side leg;

c. a second cutout portion in the same one of said side legs on the opposite side of said center leg defined by a path which extends from a predetermined point along the inner surface of said side leg proximate and on the underside of said center leg into said side leg and away from said window a predetermined distance therealong to a point substantially plane with the inner surface of said center leg and spaced from said inner surface of said side leg; and thence back along the plane of said center leg inner surface to a point plane with the inner surface of said side legs;

(1. electrical coil means wound about said center leg situated in and substantially filling said windows;

e. an elongated strip of insulating material extending from within the first cutout portion and along the inner surface of one side leg between said surface and said coil means and then along the inner surface of said first outer leg and along the inner surface of said second side leg;

f. a second elongated strip of insulating material extending from within the second cutout portion and along the inner surface of said side leg below said center leg therealong the inner surface of said second outer leg; and thence along the inner surface of said second side leg to a point proximate and below said center leg whereby said first and second insulating layers substantially border three sides of each of said windows;

g. an insulating tube surrounding said center leg and insulating said coil from said center leg, said insulating tube being greater in length than the distance between the parallel inner surfaces of said side legs, whereby a portion thereof extends into said first and second cutaway portions.

2. A transformer comprising a magnetic core having:

a. an elongated central core leg;

b. a first yoke means forming a magnetic flux path from one end of said central core leg to the other and defining with said central core leg a first coil receiving window means;

c. a second yoke means forming a second magnetic fiux path from one end of said central core leg to the other and defining with said central core leg at least another second coil receiving window means;

d. said central core leg having a first surface bordering partially said first window means and a second surface borderingpartially said second window means;

c. said first yoke means having an inner surface bordering partially said first window means;

f. said second yoke means having an inner surface bordering partially said second window means;

g. said first yoke means having a first surface portion of its inner surface oriented substantially perpendicular to said first inner surface of said central core leg proximate the left end of said central core leg and having a second surface portion of its innersurface oriented perpendicular substantially to said first inner surface of said central core leg at the right end of said central core leg;

h. said second yoke means including a first portion of its inner surface oriented substantially perpendicular to said second inner surface of said central core leg proximate the left end of said central core leg and having a second portion of its inner surface oriented substantially perpendicular to said second inner surface of said central core leg at the right end of said central core leg;

i. a first cutout portion in said first yoke means;

j. said first cutout portion being defined by a path which extends from a predetermined point along said first surface portion of said first yoke means proximate said central core leg into said first yoke means and away from said first window for a predetermined distance and then along to a point substantially plane with said first inner surface of said central core leg spaced from said inner surface of said yoke means and thence back along the plane of said first inner surface of said central core leg to a point plane with said first surface portion of said first yoke means;

k. first cutout portion in said second yoke means proximate the same end of said central core leg as said first yoke means first cutaway portion;

1. said first cutout portion being defined by a path which extends from a predetermined point along the first surface portion of said second yoke means proximate said central core leg into said second yoke means away from said second window a predetermined distance therealong to a point spaced from said first surface portion of said second yoke means and substantially plane with the second inner surface of said central core leg; and thence back along the plane of said second inner surface of said central core leg to a point substantially plane with the first surface portion of said second yoke means;

In. electrical coil means wound about said central core leg and situated in and substantially filling said first and second window means;

n. an insulating layer extending along the inner surface of said first yoke means bordering said first window means in between said coil means and said yoke and terminating within said cutout portion;

o. a second insulating layer along the inner surface of said second yoke means bordering said second window means in between said electrical coil means and said second yoke means and terminating within said cutout portion;

p. an insulating tube surrounding said central core leg and insulating said electrical coll means from said electrical core leg; said insulating tube being of a length greater than the distance between the right and left inner surfaces of said yoke means, whereby a portion thereof extends into said first and second cutaway portion.

3. A transformer comprising:

a. a magnetic core having at least a center and outer legs spaced apart and parallel and first and second side legs spaced apart and parallel and joining with said center and ,outer legs to form a magnetic loop;

b. at least a first cutout portion in one of said side legs defined by a path which extends from a predetermined point along the inner surface of said side leg and proximate said center leg into said side leg towar the outside surface of said side leg a predetermined distance, then along to a point substantially plane with the inner surface of said center leg and spaced from the inner surface of said side leg, and thence back along the plane of said center to a point plane with the inner surface of said side leg;

c. electrical coil means wound about said center leg situated in and substantially filling the space defined by said loop;

d. an insulating layer extending from the inner surface of one side leg; between said inner surface and said coil means and thence along the inner surface of said yoke and along the inner surface of said second side leg and into said cutaway portion;

e. an insulating tube surrounding said center leg and insulating said coil from said center leg, said insulating tube being greater in length than the distance between the inner surfaces of said side legs whereby a portion thereof extends into said cutaway portion.

4. The invention as defined in claim 3 further comprising a magnetic shunt leg extending from said outer leg to within a predetermined distance of said insulating tube; wherein said coil means comprises a primary winding and a secondary winding disposed side-by-side on said center leg and wherein said magnetic shunt leg is situated spacing said primary and secondary windings.

5. The invention as defined in claim 1 wherein said electrical coil means comprises precision wound type coils.

6. The invention as defined in claim 2 wherein said electrical coil means comprise precision wound type coils. 

1. A transformer comprising: a. A magnetic core having a completed configuration of a center, first outer and second outer legs spaced apart and parallel, and a first and second side leg spaced apart, parallel, and joining with said center first and second outer legs to define at least two generally rectangular windows one above and the other below said center leg; said center first outer and said first and second side legs having an inner surface bordering one Of said windows, said central second outer and first and second side legs having an inner surface bordering said other window; b. first cutout portion in one of said side legs defined by a path which extends from a predetermined point along the inner surface of said side leg and proximate said center leg into said side leg and away from said window a predetermined distance, then along to a point substantially plane with the inner surface of said center leg and spaced from said inner surface of said side leg, and thence back along the plane of said central leg to a point plane with the inner surface of said side leg; c. a second cutout portion in the same one of said side legs on the opposite side of said center leg defined by a path which extends from a predetermined point along the inner surface of said side leg proximate and on the underside of said center leg into said side leg and away from said window a predetermined distance therealong to a point substantially plane with the inner surface of said center leg and spaced from said inner surface of said side leg; and thence back along the plane of said center leg inner surface to a point plane with the inner surface of said side legs; d. electrical coil means wound about said center leg situated in and substantially filling said windows; e. an elongated strip of insulating material extending from within the first cutout portion and along the inner surface of one side leg between said surface and said coil means and then along the inner surface of said first outer leg and along the inner surface of said second side leg; f. a second elongated strip of insulating material extending from within the second cutout portion and along the inner surface of said side leg below said center leg therealong the inner surface of said second outer leg; and thence along the inner surface of said second side leg to a point proximate and below said center leg whereby said first and second insulating layers substantially border three sides of each of said windows; g. an insulating tube surrounding said center leg and insulating said coil from said center leg, said insulating tube being greater in length than the distance between the parallel inner surfaces of said side legs, whereby a portion thereof extends into said first and second cutaway portions.
 2. A transformer comprising a magnetic core having: a. an elongated central core leg; b. a first yoke means forming a magnetic flux path from one end of said central core leg to the other and defining with said central core leg a first coil receiving window means; c. a second yoke means forming a second magnetic flux path from one end of said central core leg to the other and defining with said central core leg at least another second coil receiving window means; d. said central core leg having a first surface bordering partially said first window means and a second surface bordering partially said second window means; e. said first yoke means having an inner surface bordering partially said first window means; f. said second yoke means having an inner surface bordering partially said second window means; g. said first yoke means having a first surface portion of its inner surface oriented substantially perpendicular to said first inner surface of said central core leg proximate the left end of said central core leg and having a second surface portion of its inner surface oriented perpendicular substantially to said first inner surface of said central core leg at the right end of said central core leg; h. said second yoke means including a first portion of its inner surface oriented substantially perpendicular to said second inner surface of said central core leg proximate the left end of said central core leg and having a second portion of its inner surface oriented substantially perpendicular to said second inner surface of said central core leg at the right end of said central core leg; i. a first cutout portion in said first yoke means; j. said first cutout portion being defined by a path which extends from a predetermined point along said first surface portion of said first yoke means proximate said central core leg into said first yoke means and away from said first window for a predetermined distance and then along to a point substantially plane with said first inner surface of said central core leg spaced from said inner surface of said yoke means and thence back along the plane of said first inner surface of said central core leg to a point plane with said first surface portion of said first yoke means; k. first cutout portion in said second yoke means proximate the same end of said central core leg as said first yoke means first cutaway portion; l. said first cutout portion being defined by a path which extends from a predetermined point along the first surface portion of said second yoke means proximate said central core leg into said second yoke means away from said second window a predetermined distance therealong to a point spaced from said first surface portion of said second yoke means and substantially plane with the second inner surface of said central core leg; and thence back along the plane of said second inner surface of said central core leg to a point substantially plane with the first surface portion of said second yoke means; m. electrical coil means wound about said central core leg and situated in and substantially filling said first and second window means; n. an insulating layer extending along the inner surface of said first yoke means bordering said first window means in between said coil means and said yoke and terminating within said cutout portion; o. a second insulating layer along the inner surface of said second yoke means bordering said second window means in between said electrical coil means and said second yoke means and terminating within said cutout portion; p. an insulating tube surrounding said central core leg and insulating said electrical coil means from said electrical core leg; said insulating tube being of a length greater than the distance between the right and left inner surfaces of said yoke means, whereby a portion thereof extends into said first and second cutaway portion.
 3. A transformer comprising: a. a magnetic core having at least a center and outer legs spaced apart and parallel and first and second side legs spaced apart and parallel and joining with said center and outer legs to form a magnetic loop; b. at least a first cutout portion in one of said side legs defined by a path which extends from a predetermined point along the inner surface of said side leg and proximate said center leg into said side leg toward the outside surface of said side leg a predetermined distance, then along to a point substantially plane with the inner surface of said center leg and spaced from the inner surface of said side leg, and thence back along the plane of said center to a point plane with the inner surface of said side leg; c. electrical coil means wound about said center leg situated in and substantially filling the space defined by said loop; d. an insulating layer extending from the inner surface of one side leg; between said inner surface and said coil means and thence along the inner surface of said yoke and along the inner surface of said second side leg and into said cutaway portion; e. an insulating tube surrounding said center leg and insulating said coil from said center leg, said insulating tube being greater in length than the distance between the inner surfaces of said side legs whereby a portion thereof extends into said cutaway portion.
 4. The invention as defined in claim 3 further comprising a magnetic shunt leg extending from said outer leg to within a predetermined distance of said insulating tube; wherein said coil means comprises a primary winding and a secondary winding disposed side-by-side on said center leg and wherein said magnetic shunt leg is siTuated spacing said primary and secondary windings.
 5. The invention as defined in claim 1 wherein said electrical coil means comprises precision wound type coils.
 6. The invention as defined in claim 2 wherein said electrical coil means comprise precision wound type coils. 